AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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The Transfer Function of a Drift Tube Ion Mobility Spectrometer-CPC System
DAVID BUCKLEY, Christopher Hogan Jr., University of Minnesota
Abstract Number: 27 Working Group: Instrumentation and Methods
Abstract Drift tube – ion mobility spectrometers (DT-IMSs) are often used to rapidly characterize gas phase ions via high resolution mobility separation in time. Recent work in coupling an atmospheric pressure drift tube to a condensation particle counter (CPC) has enabled mobility separation and detection of singly charged nanoparticles up to 40 nm in mobility diameter. Beyond separation, important in nanoparticle analysis is determination of the true size or mobility distribution of the original aerosol, defined as the particle concentration per unit mobility/size. However, distribution function determination requires a priori knowledge of the DT-IMS-CPC transfer function. The transfer function wholly describes the mobility-dependent transmission of the measurement system. Motivated by the need for fast, high resolution size distribution characterization of nanoparticles in the 2 – 40 nm range, the transfer function of the DT-IMS-CPC was inferred via a unique application of the Twomey-Markowski algorithm to tandem mobility measurements. Specifically, the DT-IMS-CPC system was used to measure monodisperse particles exiting a well-characterized DMA set as a mobility filter. DT-IMS-CPC measurements were performed for a range of DMA-selected mobilities, and the Twomey-Markowski algorithm was employed to invert the transfer function at specific DT-IMS-CPC measurement times over this range of mobilities. Examination of the inverted transfer functions reveals DT-IMS-CPC system resolving power more than 10 and reaching 20 for nanoparticles in the studied size range. Previous model estimates agree well with these determined resolving powers.